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Abstract Late Mesoproterozoic to Neoproterozoic sedimentary sequences within the Lake Superior region preserve critical paleogeographic records of the position of Laurentia spanning from the end of Midcontinent Rift extension through to the end of the Grenvillian Orogeny. Temporally calibrated paleomagnetic poles from these sequences are essential for resolving Laurentia's plate motion during these tectonic events. The 5 km thick ca. 1,080 to 1,045 Ma fluviolacustrine Oronto Group was deposited during thermal subsidence following rifting prior to onset of Grenvillian contractional deformation in the region. Prior paleomagnetic work has focused on the basal Freda Formation (ca. 1,075 Ma) leaving a long temporal gap in poles from that time until the ca. 990 Ma pole of the unconformably overlying Jacobsville Formation. A new U‐Pb detrital zircon maximum depositional age for the upper Freda Formation of 1,051.6 1.1 Ma indicates that Oronto Group deposition was prolonged. We have developed new inclination‐shallowing corrected paleomagnetic data from the Freda Formation that can be temporally calibrated within this improved chronostratigraphic framework. A new pole from the ca. 1,045 Ma upper Freda Formation is similar in position to that from the ca. 1,075 Ma lower Freda Formation. These data indicate that Laurentia's rapid motion of 20 cm/year from ca. 1,110 to 1,080 Ma significantly slowed to 2 cm/year following onset of the continent‐continent collision of the Grenvillian orogeny. These dynamics are what is predicted if the rapid motion was associated with differential plate tectonic motion that closed an ocean basin leading up to collisional orogenesis and the associated assembly of Rodinia.
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Tracking Rodinia Into the Neoproterozoic: New Paleomagnetic Constraints From the Jacobsville Formation
Abstract The paleogeography of Laurentia throughout the Neoproterozoic is critical for reconstructing global paleogeography due to its central position in the supercontinent Rodinia. We develop a new paleomagnetic pole from red siltstones and fine‐grained sandstones of the early Neoproterozoic Jacobsville Formation which is now constrained to be ca. 990 Ma in age. High‐resolution thermal demagnetization experiments resolve detrital remanent magnetizations held by hematite. These directions were reoriented within siltstone intraclasts and pass intraformational conglomerate tests—giving confidence that the magnetization is detrital and primary. An inclination‐corrected mean paleomagnetic pole position for the Jacobsville Formation indicates that Laurentia's motion slowed down significantly following the onset of the Grenvillian orogeny. Prior rapid plate motion associated with closure of the Unimos Ocean between 1,110 and 1,090 Ma transitioned to slow drift of Laurentia across the equator in the late Mesoproterozoic to early Neoproterozoic. We interpret the distinct position of this well‐dated pole from those in the Grenville orogen that have been assigned a similar age to indicate that the ages of the poles associated with the Grenville Loop likely need to be revised to be younger due to prolonged exhumation.
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- Award ID(s):
- 1847277
- PAR ID:
- 10489959
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Tectonics
- Volume:
- 43
- Issue:
- 2
- ISSN:
- 0278-7407
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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